FUNCTIONAL-EVALUATION OF INTERNAL MAMMARY ARTERY BYPASS GRAFTS IN THEEARLY AND LATE POSTOPERATIVE PERIODS

Objectives. We sought to determine whether internal mammary artery gra fts adapt to an increase in myocardial how demand and whether they res tore maximal flow reserve. Background. Although mammary grafts are now considered the graft of choice for coronary artery bypass surgery, th ere is still controversy about whether they can provide adequate bow a t periods of peak myocardial demand. Methods. Of 28 patients with a ma mmary graft anastomosed to the left anterior descending coronary arter y, 15 were studied early (mean [+/-SD] 8 +/- 2 days) and 13 late (19 /- 15 months) after operation by quantitative angiography and selectiv e intravascular Doppler analysis at baseline, during pacing and after injection of papaverine and isosorbide dinitrate into the graft. Eleve n patients with a normal left anterior descending artery served as con trol subjects. Results. At baseline, mean graft diameter (2.39 +/- 0.4 1 vs. 2.42 +/- 0.45 mm) and bypass flow (38 +/- 22 vs. 30 +/- 12 ml/mi n) were similar in the early and late postoperative periods. Significa nt and similar vasodilation was observed in mammary grafts after admin istration of papaverine (+6 +/- 5% vs. +9 +/- 6%) and nitrates (+14 +/ - 7% vs. +16 +/- 9%) both early and late after bypass surgery. Graft d iameter increased during pacing late (+6 +/- 3%, p < 0.05) but not ear ly after operation. Bypass flow increased similarly during pacing in b oth groups, but maximal flow reserve induced by papaverine was signifi cantly lower in mammary grafts studied early (2.70 +/- 0.62) than thos e studied late (3.66 +/- 0.81, p < 0.01) and in normal coronary arteri es (4.05 +/- 0.96, p < 0.001). Conclusions. An increase in myocardial blood flow induced by pacing resulted in vasodilation of mammary graft s in the late but not in the early postoperative period. Significant v asodilation of mammary grafts after papaverine and isosorbide dinitrat e admin istration was observed both early and late after operation. Ho wever, bypass how reserve after papaverine injection was significantly lower in the early postoperative period but normalized over time. Thi s finding seems unrelated to the conduit; rather, it appears to be rel ated to the periphery and could be the result of injury to the microva sculature during operation.